fix: resolver-based nginx config and env vars for template configs

- Use Docker embedded DNS (127.0.0.11) with variables in proxy_pass
  instead of upstream blocks to prevent nginx crash loops when
  backend isn't ready during startup
- Add STACK_NAME env to web and livekit services for golang
  template_driver config resolution
- Add LIVEKIT_API_KEY env to livekit service for config template
- Add livekit_as secret to livekit service
- Increase web healthcheck retries and start_period
- Bump NGINX_CONF_VERSION to v2

abra.sh

@@ -1,7 +1,7 @@
 # Set any config versions here
 # Docs: https://docs.coopcloud.tech/maintainers/handbook/#manage-configs
 export ABRA_ENTRYPOINT_VERSION=v1
-export NGINX_CONF_VERSION=v1
+export NGINX_CONF_VERSION=v2
 export PG_BACKUP_VERSION=v1
 export MIGRATE_VERSION=v1
 export LIVEKIT_CONFIG_VERSION=v1